Funding: DFG SPP 2289

Contact: Marc Weirich

The scope of this project is the development and description of a heteroaggregation process of different submicron particles by mixing and desublimation in an supersonic flow. The generated particles will be used to produce tailor-made surface coatings. Both the particle generation and the surface coating will be investigated with experimental and theoretical analysis. The heteroaggregates are produced in the gas phase by a heterogeneous desublimation process. A dispersed material is sublimated in the gas phase by a high-powered tube furnace before the gas mixture is expanded in a lava nozzle to form a supersonic flow. The strong and sudden drop in pressure and temperature causes the gas phase to become saturated and the released material to desublimate onto seed particles. These seed particles are guided through the areas of highest saturation in the backflow area of the laval nozzle. The mixing behaviour of the components as well as their shape and size determine the result of the aggregation process. Experiments are carried out with TiO2, Al2O3, SiO2 and hydroxyapatite (HO) as seed particles and copper phthalocyanine, Paliogen Red L4120 and silver as coating material. The heteroaggregates produced will be characterised according to their size distribution using scanning mobility particle sizer (SMPS) and scaning electron microscopy (SEM). In addition, the particle shape is determined online during the experiment with a 3D light scattering sensor. For this purpose, the aerodynamic focussing for the transfer of single particles through the measuring volume of the sensor and the laser beam guidance will be revised. The hardware of the measurement system will be upgraded to enable online measurements. The measuring capability of the system will be demonstrated by a measuring series with different test aerosols, e.g. salt crystals, polystyrene monospheres and SiO2 agglomerates. The complex flow behaviour is investigated by means of multi-scale simulations with CFD and Discrete Element Method (DEM). The deformation and fracture behaviour will be measured by nanoindentation and simulated by DEM. The formulated heteroaggregates are used in this project for the production of heterogeneous coatings by a cold spray deposition process. The functional properties of the surface are determined by nanoindentation of the generated porous coatings.